Electrostatic chucks are used to hold semiconductor wafers and other substrates during processing such as plasma etching. An electrostatic chuck (ESC) uses an electrostatic potential to hold (clamp) a substrate in place during processing. By clamping the substrate to the chuck, a high thermal conductivity gas such as helium (He) may be disposed between the substrate and the chuck in order to improve heat transfer between the substrate and the chuck. The substrate is removed from the ESC by lift pins and a transfer arm removes the substrate from the processing chamber.
A difficulty that arises with the use of an ESC is the need for removal of the residual electrostatic force between the substrate and the chuck in order to remove the substrate from the chuck. This residual force results from the accumulation of electric charge at the interface between the substrate and the ESC support surface. Several techniques have been developed for removing or de-chucking a substrate. For example, the electrode can be grounded or, alternatively, the polarity of the chucking voltage applied to the electrode can be reversed in order to discharge the electrode. However, these techniques are not completely effective at removing all the charge on the electrode and the substrate. A mechanical force is often required to overcome the residual attractive electrostatic force, which can damage the substrate or create difficulty in retrieving the substrate from an unintended position. Further, undesired particles can be generated during the substrate dechucking and removal process which contaminate the processed substrate.
Despite the developments to date, there is an interest in apparatus and methods which reduce any voltage potential spike during dechucking of processed substrates.